1. Field of the Invention
The present invention relates to a door sensor for a domestic appliance and, more particularly, to a new and improved fiber optic sensor for a domestic appliance, the sensor determining whether a door or doors of the appliance are open or slightly ajar.
2. Description of the Prior Art
In a domestic appliance such as a refrigerator/freezer, a refrigerator door is hingedly mounted along one edge of the refrigerator/freezer in order to permit access into and to seal a refrigerator compartment or section. In a similar manner, a freezer door is hingedly mounted along one of the side edges of the refrigerator/freezer in order to permit access into and to seal a freezer compartment or section. If one of these doors is left open or slightly ajar, the compartment is no longer properly sealed requiring an excessive amount of energy to be used to maintain the compartment at the proper temperature level to prevent food stored therein from spoiling.
Various types of sensors have been used in such appliances to determine if one of the doors has been left open or slightly ajar and to activate a visual and/or audible warning signal if the door is so open. One such sensor includes a plunger that protrudes from the front frame of the refrigerator cabinet. When the door is properly closed, the plunger is depressed and maintains contacts within a microswitch in a non-actuated state. In the event the door is opened, the plunger protrudes from the front frame of the refrigerator actuating the microswitch which in turn causes the interior lights of the refrigerator to turn on and/or provides a door open signal. Plunger type sensor arrangements have moving parts which may be adversely affected by the accumulation of dirt or debris. Moreover, if the microswitch used in such plunger type arrangements is operated at a low voltage or current, the microswitch becomes relatively expensive for use in an appliance.
Magnetic sensing devices have also been used in a refrigerator to determine whether a door is open. In such a device, a magnet is mounted on the frame of the refrigerator and a magnetic sensor is positioned on the interior face of the refrigerator door. When the door is opened, the magnet is moved away from the magnetic sensor and a switch associated with the magnetic sensor is activated to provide a door open signal. While these magnetic sensing devices tend to be less expensive and less sensitive to dirt problems than the plunger type arrangements, they typically do not accurately sense when a door is left only slightly open or ajar.
In order to overcome the problems associated with the plunger and magnetic sensing devices, magnetic field responsive switches, for example Hall effect sensors, have been used. In U.S. Pat. No. 4,241,337, such a magnetic field responsive switch is disclosed for determining when a refrigerator door is open or closed. A similar sensing device is disclosed in U.S. Pat. No. 4,074,246 wherein audio frequency transducers are used to detect when a window or door has been opened. U.S. Pat. No. 4,074,246 alternatively discloses the use of an infrared transmitter and receiver interconnected by a mirror to provide an alarm when a door or window is left open.
Various other arrangements have been used to detect the movement or displacement of different types of objects. For example, in U.S. Pat. No. 3,544,988, the movement of an object is sensed by having an illuminator portion of an infrared sensor project a beam of infrared radiation to a cylindrical mirror mounted on an object whose displacement is to be detected. The infrared radiation is reflected by the mirror to a receiver located in a common housing with the illuminator. When the object is moved, an alarm signal is activated. A similar position detector is disclosed in U.S. Pat. No. 4,507,654 wherein an infrared tranmitter and an infrared detector are used for determining whether a door or window is ajar. The infrared light produced by the transmitter is pulsed and is reflected onto a receiver by a reflector affixed to the door or window. When the pulsed light being received is not coincident with a pulse signal from a pulse generator, an alarm is activated to indicate that the door or window is open. U.S. Pat. No. 4,583,082 also relates to an apparatus for monitoring whether a door of a coin operated machine is open or closed, the apparatus including a light emitting diode and an aligned photocell sensor wherein a microprocessor monitors the light emitting diode and the photocell sensor to provide an alarm signal when the two are not in optical communication.
Another door monitoring apparatus is disclosed in U.S. Pat. No. 3,909,819. In that patent the door being monitored is the door of a mailbox. A photocell is mounted in the mailbox such that if the door of the mailbox is opened, the external ambient light entering the mailbox is detected by the photocell. Upon the detection of external light an indication of the opening of the mailbox door is provided. An intrusion detector is disclosed in U.S. Pat. No. 4,013,886, in which a light transmitter and receiver are mounted on a common body. If an object intrudes into the path of the light beam being projected from the transmitter to the receiver, a warning signal is provided.
An example of how fiber optics may be used to actuate a switch when moved in alignment with a sensor is shown in U.S. Pat. No. 4,631,399. More specifically, the patent shows a switch having an array of phototransistors each representing a selectable switch position wherein a selectively rotatable fiber optic is used to transmit light from a light emitting diode to one of the phototransistors to cause it to conduct current to a keyboard encoder.